1. Technical Field
The present invention relates to an overcoat composition for electrophotography, an electrophotographic image forming method and an electrophotographic image forming apparatus.
2. Description of the Related Art
On-demand printing is extensively applied recently, which responds to recent demand for rapid output of variable information. On-demand printing apparatuses are of two main types: electrophotographic apparatuses and inkjet apparatuses. In particular, electrophotographic apparatuses that reproduce image information with toner are more widely used.
An electrophotographic apparatus is generally equipped with a fixing device that fixes toner on a recording medium with a fixing roller. The fixing roller is applied with a large amount of oil so that the toner is easily releasable from the fixing roller. There have been a problem that the oil undesirably contaminates the recording medium and another problem that the fixing device becomes more expensive, more complicated, and larger due to installation of an oil container.
In view of this situation, a more simplified fixing device which does not use oil (hereinafter “oilless fixing device”) is strongly needed. Simultaneously, a toner applicable to the oilless fixing device is also needed. In response to this need, a toner including a wax has been proposed.
Brochures and book covers printed by on-demand printing sometimes need to be protected from water or contamination or to have appropriate gloss depending on their purpose of use. In these cases, a transparent layer is formed on the printed surface. The transparent layer may be formed on the printed surface by, for example, overcoming, vinyl coating, press coating, or film pasting. Among these various processing procedures, overcoating with a varnish is widely preferred for its simplicity.
As to overcoating technique in electrophotography, Japanese published unexamined application No. JP-2007-277547-A describes a water-based ammonia-free varnish composition having a low static surface tension for overcoating printed materials on which a fixing oil is applied.
Japanese published unexamined application No. JP-H10-309876-A describes an image forming apparatus including a resin layer forming device that forms a silicone resin layer on a printed surface.
Japanese Patent No. JP-2522333-B1 (Japanese published unexamined application No. JP-H01-163747-A) describes an electrophotographic printing method applicable to metal containers.
In the above-described techniques, however, there is a limit in choosing a suitable combination of a toner composition and an overcoat composition. Even in a case in which an overcoat composition can be applied to a toner image formed on a recording medium, the resulting overcoat layer sometimes peels off from the toner image due to weak adhesion. In particular, when the toner includes a wax, peeling off of the overcoat layer significantly occurs. In some cases, the overcoat composition is repelled from the toner image and cannot be applied to the toner image.
Because of these reasons, a need exist for an overcoat composition for electrophotography, adhering to toner images without repelling.